Recently, developments are being made to obtain high-performance devices in the field of display-apparatus thin-film semiconductor devices which are drive substrates of display apparatuses such as organic electroluminescence displays and liquid crystal displays. The screen of a display apparatus has been increased in size following the progress of manufacturing process technique, and furthermore there is a demand from customers for high-quality display apparatuses with a large screen. Following the increase in the screen size and quality of display apparatuses, there is a demand for high current drive capacity of thin-film transistors included in display-apparatus thin-film semiconductor devices. In particular, attention has been brought to a thin-film transistor which uses, as an active layer, a crystallized semiconductor thin film (such as polycrystalline silicon or microcrystal silicon).
Conventionally, a thin-film transistor used in a display-apparatus thin-film semiconductor device is a field effect transistor which includes: three electrodes, namely, a gate electrode, a source electrode, and a drain electrode; a gate insulating film; and a semiconductor layer. A line made of a conductor for driving a thin-film transistor (many of such conductors are made of metal or metal oxide) is connected to each of the electrodes. These lines are formed above a substrate in a matrix having m rows and n columns, and the lines cross three-dimensionally.
In crossing areas where the lines in m rows and the lines in n columns cross, short circuits in the crossing of the lines in m rows and the lines in n columns are each prevented by interposing, in the same layer, a film obtained by extending the gate insulating film. Consequently, the crossing lines in m rows and n columns are close to one another, thus resulting in parasitic capacitance between the lines. The amount of parasitic capacitance depends on the distance between crossing lines, a specific inductive capacity unique to a substance in the layer interposed between lines, or the like. The parasitic capacitance will be accumulated if the size of a display apparatus is increased, resulting in a delay of a driving signal. In addition, an increase in a drive frequency to improve quality also increases the impedance of a circuit due to parasitic capacitance. Specifically, an increase in the size of a display apparatus and improvement in the quality thereof makes the problem of parasitic capacitance more serious.
To address such a problem, for example, in line crossing areas, the width of the crossing lines in m rows and n columns are narrowed, thereby decreasing areas in which the crossing lines in m rows and in n columns overlap. A technique for reducing parasitic capacitance between lines by decreasing the areas in which the crossing lines overlap in the above manner is disclosed (e.g., Patent Literature (PTL) 1).